Milk as a rehydration fluid following exercise-induced loss of body mass.

The effectiveness of 0.1% fat milk (M) at restoring fluid balance after exercise and heat induced hypohydration was compared to a commercially available carbohydrate-electrolyte (CE) sports drink and water (W) using a metered rate of fluid ingestion. After losing 2.1 (0.2) % body mass, participants (n = 7) consumed a drink volume equivalent to 150% of their body mass loss, over a period of 2.5-3 hours. A metered rate of fluid ingestion was chosen as it is widely acknowledged that rapid ingestion (< 60 min) of a large volume of fluid (>1000ml) can over-stimulate diuresis. Blood and urine samples were collected before and for 5 hours after exercise-induced loss of body mass. Mean plasma osmolality was higher in the M trial 289 (3) mOsmol/kg compared to W 286 (3) mOsmol/kg and CE 287 (3) mOsmol/kg, during this 5 hour period (p = 0.021). Indicative of a reduced diuretic response, urine volume was lower and urine osmolality higher in the M trial compared with CE and W. Total urine volume during the M trial was 774 (92) mL compared to CE 1314 (434) mL and W 1429 (345) mL (p = 0.023). A net positive fluid balance from 2h to 5h was achieved in the M trial, whereas the CE and W trials returned to net negative balance by the end of the 5h rehydration period. Final net fluid balance in the M trial was 117 (122) mL compared to CE -381 (460) mL and W trials -539 (390) mL (p = 0.049). This represents a final relative net fluid balance of 5.9 (5.9) % in the M trial compared with CE -22.7 (23.3) % (p = 0.048) and W - 30.9 (22.7) % (p = 0.012).